The invention relates to stock feed apparatus for feeding strip stock to or from a stock processing machine to maintain a loop in the stock.
In the feeding of strip stock to or from a stock processing machine such as a punch press, it is common practice to operate the stock feed means to maintain a slack loop in the stock in order to accommodate the intermittent transfer of the stock through the processing machine. The stock feed apparatus may comprise a power operated stock payout or rewind reel that effects advance of stock by winding or unwinding stock from a coil. The stock advancing apparatus can also comprise powered stock feed rollers or powered stock straightening rollers.
Various systems have heretofore been made for sensing the size of the stock loop and for driving the stock feed apparatus in a manner to maintain the stock loop between predetermined limits. In some, such as disclosed in U.S. Pat. No. 4,578,621, a stock loop sensor in the form of a dancer arm is arranged to sense the size of the stock loop and produce an analog control voltage for driving the stock feed apparatus at a speed proportional to the size of the stock loop, to maintain the stock loop within predetermined limits. Stock feed controls have also been made in which the stock loop sensor provides a digital signal when the stock loop exceeds a predetermined minimum and maximum size limits. Some prior stock feed apparatus having digital input utilize the digital input signals to start the stock feed apparatus when the stock reaches a predetermined minimum limit and to stop the stock feed apparatus when the stock loop reached a predetermined maximum limit. However, because of the rapid advance of the stock through the stock processing machine, it is necessary to rapidly cycle such on/off feed controls. It has also been proposed, as disclosed in U.S. Pat. No. 3,637,123, to provide a stock feed apparatus having a photoelectric loop size sensor for sensing when the loop size increases or decreases relative to a reference size, and which produces an alternating on/off signal having a frequency determined by the number of times the size of the loop increases or decreases relative to the reference size, with means for converting the on/off signal to an analog signal proportional to the frequency of the on/off signal, and means responsive to the analog signal for adjusting the speed of the feed means to maintain the size of the slack loop between predetermined limits.